This excerpt taken from the MTA 20-F filed Feb 22, 2007.
Volume-dependent ADSL. On February 1, 2005, we introduced a new wholesale ADSL billing concept, the volume-based billing. Our ISP partners can now choose between flat rate billing and volume-based billing. In case of volume-based billing the monthly fee of the wholesale ADSL consists of access fee and traffic charges, based on the volume of the ADSL user traffic. This new pricing structure enable the ISP partners to offer a much wider choice of services better suited to the end users requirements.